1. Field of the Invention
The present invention is directed to a method and apparatus for blast freezing or thawing a frozen commodity such as a food product.
2. Description of Background Art
It is common in the food industry to use a blast freezer to freeze various food products. Normally, a blast freezer requires the use of an expensive specially designed tunnel in which food products are positioned on pallets within the tunnel. The tunnel is built in a freezer that is maintained at a temperature of approximately −40° Fahrenheit (−40° Celsius). Air is blown or pushed onto the food products disposed in the tunnel to freeze the food products. However, as the cold air is first blown or pushed towards the first pallet of food products to be frozen, the air is warmed by the temperature of the food products so that the second pallet in the row is exposed to a warmer air as compared to the first pallet of food products. This problem is exacerbated as air is blown or pushed towards the third pallet and thereafter the fourth pallet and subsequent pallets. Thus, the food products positioned on the last pallet will be frozen at a different time as compared to food products disposed directly adjacent to the air handler. After the food products are frozen, the food products are transferred to a freezer that is maintained at a temperature of approximately −20° Fahrenheit (−28.88° Celsius) or at a temperature of approximately −10° Fahrenheit (−23.33° Celsius).
A similar problem occurs when it is desired to thaw the food products. For example, the food products may be positioned on a loading dock and subjected to ambient air to thaw the food products. Normally, a plurality of pallets of food products are arranged on the loading dock or in a warehouse and ambient air is blown or pushed towards the pallets. If the ambient air is at 72° Fahrenheit (22.22° Celsius), the first pallet of food products will thaw first and may reach a temperature above the mandated safety zone of 40° Fahrenheit (4.44° Celsius). The thawing of the food products on a loading docket or in a warehouse may lead to the growth of bacteria in the food products that may be transmitted to contaminate adjacent food products and other areas of the warehouse. In addition, the thawing of a food product in this manner may lead to the discoloration of the food product. Further, the food products will be thawed unevenly and thus lead to problems in determining which food products are properly thawed for delivery to a customer. Still further, the thawing of a frozen food products in ambient air leads to the production of condensation within the boxes of the food products. This will produce a wet or soggy box with a wet food product that is not suitable for delivery to a customer.
Another way to thaw a food product is to position the food product in a cooler that is maintained at a temperature of approximately 37° Fahrenheit (2.77° Celsius). Again the pallets of food products have air that is blown or pushed towards the pallets. The pushing of the air unto the pallets of food products will lead to the thawing of the food on the pallet that is located immediately adjacent to the air handler. Pallets of food products that are displaced away from the first pallet will be thawed at a different rate. It is difficult to determine when the various pallets of food products are properly thawed. Uneven thawing will lead to the need to use a longer time to thaw the food products. By using the conventional blowing or pushing of air method towards the food products, it takes approximately 7 to 10 days to thaw a frozen food product, such as ham or turkey, in a cooler.